Loading/unloading mechanisms have been developed for loading/unloading cassettes through an introduction slot, e.g. as disclosed in U.S. Pat. No. 5,314,141, in which a housing receives a cassette, the housing performing a horizontal, then a vertical movement. Such mechanisms have proven to be poorly suited to operate with different size cassettes having a substantial discrepancy in width because when a large-size cassette is securely held in the housing, then the edge of a small-size cassette barely protrudes from it and thus proves difficult to be gripped by the user or when the edge of a small-size cassette protrudes sufficiently so that the cassette can easily be gripped at the edge by the user, then the large-size cassette is not securely held in the unit because of a very large overhang. In addition, the device actuating the elements of the unit to be adapted to the size of the inserted cassette can be positioned only laterally with respect to the housing holding the cassette, something not always convenient. Further, the different cassettes of a same family must have almost the same thickness.
To deal with such drawbacks, housings have been designed for undergoing a single movement to transfer the cassette to its operative position. For example, German application DE 33 27 403 discloses a device including a mechanical feeler mounted in the housing receiving the cassette, the housing performing just a vertical movement; U.K. application 2,164,193 discloses a mechanism embodying rails linked by a parallelogram linkage which can be displaced for scanning the format of the cassette inserted in a cover which is then pivoted. Such housings either incorporate a rather complex mechanism to scan the format or size of the inserted cassette or the too long length of their stroke, which is required for adjusting components of the unit; accordingly, mechanisms with such housing are objectionable because of complexity or cost.
In order to overcome the above-mentioned draw-backs, one loading/unloading system has been proposed embodying a "drawer" incorporating either a dedicated housing for each size of cassettes such as disclosed in the European application EP 0 398317 or a single housing which incorporates positioning and/or driving means for a small-size cassette such as described in the European application EP 0 415411. Such loading/unloading systems respectively occupy too large a volume and are rather complicated and accordingly, neither has achieved significant commercial success.